The invention relates to the rapid and noninvasive measurement of polycarbonate composition. In particular, the method describes determination of the concentration of total Fries rearrangement products, or their separate linear and branched components, as well as uncapped phenolic end-groups, by a combination of UV/visible absorbance spectroscopy and multivariate data analysis.
The melt (LX) polymerization process utilizing bisphenol A (BPA) and diphenyl carbonate (DPC) is one of the most efficient non-phosgene routes of polycarbonate production. Still, the formation of Fries rearrangement products during melt polymerization can be problematic. Fries rearrangement products result from the conversion of phenolic esters into corresponding ortho and para hydroxyketones as a result of the inherent stability of polybenzenoid compounds. Polycarbonates produced by the melt process typically have higher Fries content than polycarbonates produced by the interfacial method. Excess Fries product can lead to differences in physical properties, such as flow and ductility, between polycarbonate produced by the melt process and polycarbonate produced by more traditional interfacial methods. It is important, therefore, to monitor and control for excess Fries produced during polymerization. In addition, in many cases it is also important to monitor the amount of xe2x80x9cuncappedxe2x80x9d polymer chains. Uncapped polymer chains are those chains which terminate in a free phenolic group, as opposed to being terminated with an aryl carbonyl group. It has been found that the hydrolytic stability of polycarbonate is inversely proportional to the amount of uncapped chain ends. Thus, a method which provides accurate analysis of Fries products and the amount of uncapped chain ends would be of value for the optimization of polymerization reaction conditions, both in the research setting and for on-line monitoring at the production scale.
Conventional techniques for monitoring Fries products generally involve analyzing aliquots from the reaction mixture by methods such as liquid chromatography (LC), or nuclear magnetic resonance (NMR). Similarly, techniques employed for the analysis of phenolic end-groups include IR spectroscopy, proton NMR, and potentiometric titration. These and other known methods of laboratory analysis, however, are time consuming and/or require relatively large sample sizes. Furthermore, these methods are not well-suited to on-line analysis of polycarbonate formed during large-scale production in that they require multiple sample preparation steps which are time-consuming, add to the overall error, are potentially dangerous at the high temperatures used for polymerization, and are not easily adaptable for remote monitoring using optical fibers. Also, removing aliquots may alter the reaction conditions or sample constitution, and provides only temporally discrete data points, rather than a continuous profile.
As an alternative to monitoring reactions during the polymerization, samples may be analyzed after the reaction is complete, and unsatisfactory products discarded. For example, a known technique for monitoring phenolic end-groups employs ultraviolet (UV) absorption spectroscopy to measure absorbance of phenolic end-groups at about 287 nm. Another technique for monitoring phenolic end-groups employs ratiometric ultraviolet absorption spectroscopy where absorbance of carbonate units in the spectral region of about 266 or 272 nm is compared to the absorbance of phenolic end-groups at about 287 nm. The measurements are typically performed by dissolving the polymer in a suitable solvent followed by UV spectrophotometric analysis or by a gel permeation chromatography and UV analysis (E. Shchori and J. E. McGrath, J. Appl. Polym. Sci., Appl. Polym. Symp., 34:103-117 (1978); and C. O. Mork and D. B. Priddy, J. Appl. Polym. Sci., 45:435-442 (1992). Post-reaction sampling, however, does not enable real-time optimization of reaction parameters and, therefore, may result in the synthesis of a polymer batch of substantially inferior quality.
Thus, there is a need for noninvasive methods for monitoring levels of linear and branched Fries rearrangement products and phenolic end-groups for polycarbonate synthesis reactions. Reaction monitoring should be independent of reaction variables unrelated to the reaction component of interest, such as the starting materials and catalysts used, as well as reaction parameters such as final polymerization temperature, reactor design, and product molecular weight. As there is a continuing need to evaluate economically superior reactant systems, the method should be adaptable to combinatorial (small-scale) evaluation of new reactant and catalyst combinations, as well as on line monitoring of large-scale production systems.
The present invention is directed to a method for monitoring polymerization reactions and reaction components using electronic absorbance spectroscopy. The invention provides methods for the analysis of linear and branched chain Fries products and phenolic end-groups formed during polymer synthesis, as for example, during the production of polycarbonate by melt polymerization. The methods of the present invention are non-invasive, and suitable for small-scale combinatorial formats as well as large-scale production monitoring.
Thus, in one aspect, the invention comprises a method for monitoring polymer composition comprising irradiating a sample comprising at least one polymer and/or oligomer with at least one substantially monochromatic radiation, monitoring UV/visible light absorbed by the irradiated sample, and correlating the light absorbed by the irradiated sample to at least one pre-determined reaction component, wherein one of the predetermined reaction components comprises Fries products.
In another aspect, the present invention comprises a method for monitoring polycarbonate composition comprising irradiating a polycarbonate sample comprising polymer and/or oligomer with at least two wavelengths of substantially monochromatic radiation, monitoring UV/visible light absorbed by the irradiated polycarbonate, and correlating the light absorbed by the irradiated polycarbonate to Fries products and un-capped phenolic end-groups in the irradiated polycarbonate.